1. Field of the Invention
This invention relates to moisture separator reheaters and more particularly to improved reheaters for moisture separator reheaters used in steam turbine power plants.
2. Description of the Prior Art
In large steam turbine power plants where a series of turbine stages are employed, it is often desired to treat the steam exiting one of such turbine stages before that steam enters a succeeding stage. The steam is treated to remove any moisture entrained therein, and to reheat the steam to higher temperatures.
Moisture separator reheaters of various types are well known in the prior art. One example of such moisture separator reheaters is disclosed in U.S. Pat. No. 3,712,272, Carnavos et al, assigned to the assignee of the present invention. The moisture separator reheater disclosed in the Carnavos et al patent employs two reheater sections each of which comprises a bank or bundle of U-shaped tubes extending longitudinally within a pressure-tight shell and including a header for introducing a reheating fluid (steam) to the tubes and withdrawing the fluid (condensate) from the tubes. The Carnavos header is provided with a vertical baffle disposed substantially at the middle thereof dividing the header into inlet and outlet sections. Each tube has one end communicating with the inlet section and another end communicating with the outlet section. In operation, saturated reheating steam is fed to the U-shaped tubes through the inlet section of the header, traverses the tubes, and exits the tubes through the outlet section of the header, any condensate formed in the reheater tubes being drained through a single drain provided in the outlet section.
Under certain operating conditions, substantial quantities of the reheating steam may condense within the lower, thermally, highly loaded U-shaped tubes and collect within the outlet section of the header to the extent that there is a build-up of the condensate therein. Such a build-up of condensate within the header may cause flooding of the tubes. During the operation of the moisture separator reheater, the flooded tubes may purge themselves and may then again become flooded. This cyclic flooding and purging of the tubes causes thermal cycling of the tubes which effects thermal stress concentrations therein, and in time may cause rupturing of those tubes.
One prior art reheater for moisture separator reheaters described in U.S. Pat. No. 3,759,319, Ritland, dealt with the problem of tube flooding by incorporating within a header employed therewith, a mainifold arrangement for recirculating the reheating fluid from one portion of the tubes through another portion of the tubes. In this recirculation process, condensate is deposited within the manifold and drained from the manifold to the header. The condensate is drained from the header through a single drain. However, this solution to the problem necessitates a manifold and additional tubing within the header. The improved reheater of the present invention eliminates the possibility of tube flooding in a more efficient and less complicated manner.
Accordingly, it is an object of the present invention to provide an improved reheater for a moisture separator reheater which simply, efficiently and with a minimum number of added components eliminates tube flooding thereby preventing thermal cycling and possible rupture of any tubes employed therein.